net/netfilter/nft_synproxy.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/types.h>
   3 #include <net/ip.h>
   4 #include <net/tcp.h>
   5 #include <net/netlink.h>
   6 #include <net/netfilter/nf_tables.h>
   7 #include <net/netfilter/nf_conntrack.h>
   8 #include <net/netfilter/nf_conntrack_synproxy.h>
   9 #include <net/netfilter/nf_synproxy.h>
  10 #include <linux/netfilter/nf_tables.h>
  11 #include <linux/netfilter/nf_synproxy.h>
  12
  13 struct nft_synproxy {
  14         struct nf_synproxy_info info;
  15 };
  16
  17 static const struct nla_policy nft_synproxy_policy[NFTA_SYNPROXY_MAX + 1] = {
  18         [NFTA_SYNPROXY_MSS]             = { .type = NLA_U16 },
  19         [NFTA_SYNPROXY_WSCALE]          = { .type = NLA_U8 },
  20         [NFTA_SYNPROXY_FLAGS]           = { .type = NLA_U32 },
  21 };
  22
  23 static void nft_synproxy_tcp_options(struct synproxy_options *opts,
  24                                      const struct tcphdr *tcp,
  25                                      struct synproxy_net *snet,
  26                                      struct nf_synproxy_info *info,
  27                                      const struct nft_synproxy *priv)
  28 {
  29         this_cpu_inc(snet->stats->syn_received);
  30         if (tcp->ece && tcp->cwr)
  31                 opts->options |= NF_SYNPROXY_OPT_ECN;
  32
  33         opts->options &= priv->info.options;
  34         opts->mss_encode = opts->mss_option;
  35         opts->mss_option = info->mss;
  36         if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
  37                 synproxy_init_timestamp_cookie(info, opts);
  38         else
  39                 opts->options &= ~(NF_SYNPROXY_OPT_WSCALE |
  40                                    NF_SYNPROXY_OPT_SACK_PERM |
  41                                    NF_SYNPROXY_OPT_ECN);
  42 }
  43
  44 static void nft_synproxy_eval_v4(const struct nft_synproxy *priv,
  45                                  struct nft_regs *regs,
  46                                  const struct nft_pktinfo *pkt,
  47                                  const struct tcphdr *tcp,
  48                                  struct tcphdr *_tcph,
  49                                  struct synproxy_options *opts)
  50 {
  51         struct nf_synproxy_info info = priv->info;
  52         struct net *net = nft_net(pkt);
  53         struct synproxy_net *snet = synproxy_pernet(net);
  54         struct sk_buff *skb = pkt->skb;
  55
  56         if (tcp->syn) {
  57                 /* Initial SYN from client */
  58                 nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
  59                 synproxy_send_client_synack(net, skb, tcp, opts);
  60                 consume_skb(skb);
  61                 regs->verdict.code = NF_STOLEN;
  62         } else if (tcp->ack) {
  63                 /* ACK from client */
  64                 if (synproxy_recv_client_ack(net, skb, tcp, opts,
  65                                              ntohl(tcp->seq))) {
  66                         consume_skb(skb);
  67                         regs->verdict.code = NF_STOLEN;
  68                 } else {
  69                         regs->verdict.code = NF_DROP;
  70                 }
  71         }
  72 }
  73
  74 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
  75 static void nft_synproxy_eval_v6(const struct nft_synproxy *priv,
  76                                  struct nft_regs *regs,
  77                                  const struct nft_pktinfo *pkt,
  78                                  const struct tcphdr *tcp,
  79                                  struct tcphdr *_tcph,
  80                                  struct synproxy_options *opts)
  81 {
  82         struct nf_synproxy_info info = priv->info;
  83         struct net *net = nft_net(pkt);
  84         struct synproxy_net *snet = synproxy_pernet(net);
  85         struct sk_buff *skb = pkt->skb;
  86
  87         if (tcp->syn) {
  88                 /* Initial SYN from client */
  89                 nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
  90                 synproxy_send_client_synack_ipv6(net, skb, tcp, opts);
  91                 consume_skb(skb);
  92                 regs->verdict.code = NF_STOLEN;
  93         } else if (tcp->ack) {
  94                 /* ACK from client */
  95                 if (synproxy_recv_client_ack_ipv6(net, skb, tcp, opts,
  96                                                   ntohl(tcp->seq))) {
  97                         consume_skb(skb);
  98                         regs->verdict.code = NF_STOLEN;
  99                 } else {
 100                         regs->verdict.code = NF_DROP;
 101                 }
 102         }
 103 }
 104 #endif /* CONFIG_NF_TABLES_IPV6*/
 105
 106 static void nft_synproxy_do_eval(const struct nft_synproxy *priv,
 107                                  struct nft_regs *regs,
 108                                  const struct nft_pktinfo *pkt)
 109 {
 110         struct synproxy_options opts = {};
 111         struct sk_buff *skb = pkt->skb;
 112         int thoff = nft_thoff(pkt);
 113         const struct tcphdr *tcp;
 114         struct tcphdr _tcph;
 115
 116         if (pkt->tprot != IPPROTO_TCP) {
 117                 regs->verdict.code = NFT_BREAK;
 118                 return;
 119         }
 120
 121         if (nf_ip_checksum(skb, nft_hook(pkt), thoff, IPPROTO_TCP)) {
 122                 regs->verdict.code = NF_DROP;
 123                 return;
 124         }
 125
 126         tcp = skb_header_pointer(skb, thoff,
 127                                  sizeof(struct tcphdr),
 128                                  &_tcph);
 129         if (!tcp) {
 130                 regs->verdict.code = NF_DROP;
 131                 return;
 132         }
 133
 134         if (!synproxy_parse_options(skb, thoff, tcp, &opts)) {
 135                 regs->verdict.code = NF_DROP;
 136                 return;
 137         }
 138
 139         switch (skb->protocol) {
 140         case htons(ETH_P_IP):
 141                 nft_synproxy_eval_v4(priv, regs, pkt, tcp, &_tcph, &opts);
 142                 return;
 143 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 144         case htons(ETH_P_IPV6):
 145                 nft_synproxy_eval_v6(priv, regs, pkt, tcp, &_tcph, &opts);
 146                 return;
 147 #endif
 148         }
 149         regs->verdict.code = NFT_BREAK;
 150 }
 151
 152 static int nft_synproxy_do_init(const struct nft_ctx *ctx,
 153                                 const struct nlattr * const tb[],
 154                                 struct nft_synproxy *priv)
 155 {
 156         struct synproxy_net *snet = synproxy_pernet(ctx->net);
 157         u32 flags;
 158         int err;
 159
 160         if (tb[NFTA_SYNPROXY_MSS])
 161                 priv->info.mss = ntohs(nla_get_be16(tb[NFTA_SYNPROXY_MSS]));
 162         if (tb[NFTA_SYNPROXY_WSCALE])
 163                 priv->info.wscale = nla_get_u8(tb[NFTA_SYNPROXY_WSCALE]);
 164         if (tb[NFTA_SYNPROXY_FLAGS]) {
 165                 flags = ntohl(nla_get_be32(tb[NFTA_SYNPROXY_FLAGS]));
 166                 if (flags & ~NF_SYNPROXY_OPT_MASK)
 167                         return -EOPNOTSUPP;
 168                 priv->info.options = flags;
 169         }
 170
 171         err = nf_ct_netns_get(ctx->net, ctx->family);
 172         if (err)
 173                 return err;
 174
 175         switch (ctx->family) {
 176         case NFPROTO_IPV4:
 177                 err = nf_synproxy_ipv4_init(snet, ctx->net);
 178                 if (err)
 179                         goto nf_ct_failure;
 180                 break;
 181 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 182         case NFPROTO_IPV6:
 183                 err = nf_synproxy_ipv6_init(snet, ctx->net);
 184                 if (err)
 185                         goto nf_ct_failure;
 186                 break;
 187 #endif
 188         case NFPROTO_INET:
 189                 err = nf_synproxy_ipv4_init(snet, ctx->net);
 190                 if (err)
 191                         goto nf_ct_failure;
 192                 err = nf_synproxy_ipv6_init(snet, ctx->net);
 193                 if (err) {
 194                         nf_synproxy_ipv4_fini(snet, ctx->net);
 195                         goto nf_ct_failure;
 196                 }
 197                 break;
 198         }
 199
 200         return 0;
 201
 202 nf_ct_failure:
 203         nf_ct_netns_put(ctx->net, ctx->family);
 204         return err;
 205 }
 206
 207 static void nft_synproxy_do_destroy(const struct nft_ctx *ctx)
 208 {
 209         struct synproxy_net *snet = synproxy_pernet(ctx->net);
 210
 211         switch (ctx->family) {
 212         case NFPROTO_IPV4:
 213                 nf_synproxy_ipv4_fini(snet, ctx->net);
 214                 break;
 215 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 216         case NFPROTO_IPV6:
 217                 nf_synproxy_ipv6_fini(snet, ctx->net);
 218                 break;
 219 #endif
 220         case NFPROTO_INET:
 221                 nf_synproxy_ipv4_fini(snet, ctx->net);
 222                 nf_synproxy_ipv6_fini(snet, ctx->net);
 223                 break;
 224         }
 225         nf_ct_netns_put(ctx->net, ctx->family);
 226 }
 227
 228 static int nft_synproxy_do_dump(struct sk_buff *skb, struct nft_synproxy *priv)
 229 {
 230         if (nla_put_be16(skb, NFTA_SYNPROXY_MSS, htons(priv->info.mss)) ||
 231             nla_put_u8(skb, NFTA_SYNPROXY_WSCALE, priv->info.wscale) ||
 232             nla_put_be32(skb, NFTA_SYNPROXY_FLAGS, htonl(priv->info.options)))
 233                 goto nla_put_failure;
 234
 235         return 0;
 236
 237 nla_put_failure:
 238         return -1;
 239 }
 240
 241 static void nft_synproxy_eval(const struct nft_expr *expr,
 242                               struct nft_regs *regs,
 243                               const struct nft_pktinfo *pkt)
 244 {
 245         const struct nft_synproxy *priv = nft_expr_priv(expr);
 246
 247         nft_synproxy_do_eval(priv, regs, pkt);
 248 }
 249
 250 static int nft_synproxy_validate(const struct nft_ctx *ctx,
 251                                  const struct nft_expr *expr,
 252                                  const struct nft_data **data)
 253 {
 254         if (ctx->family != NFPROTO_IPV4 &&
 255             ctx->family != NFPROTO_IPV6 &&
 256             ctx->family != NFPROTO_INET)
 257                 return -EOPNOTSUPP;
 258
 259         return nft_chain_validate_hooks(ctx->chain, (1 << NF_INET_LOCAL_IN) |
 260                                                     (1 << NF_INET_FORWARD));
 261 }
 262
 263 static int nft_synproxy_init(const struct nft_ctx *ctx,
 264                              const struct nft_expr *expr,
 265                              const struct nlattr * const tb[])
 266 {
 267         struct nft_synproxy *priv = nft_expr_priv(expr);
 268
 269         return nft_synproxy_do_init(ctx, tb, priv);
 270 }
 271
 272 static void nft_synproxy_destroy(const struct nft_ctx *ctx,
 273                                  const struct nft_expr *expr)
 274 {
 275         nft_synproxy_do_destroy(ctx);
 276 }
 277
 278 static int nft_synproxy_dump(struct sk_buff *skb, const struct nft_expr *expr)
 279 {
 280         struct nft_synproxy *priv = nft_expr_priv(expr);
 281
 282         return nft_synproxy_do_dump(skb, priv);
 283 }
 284
 285 static struct nft_expr_type nft_synproxy_type;
 286 static const struct nft_expr_ops nft_synproxy_ops = {
 287         .eval           = nft_synproxy_eval,
 288         .size           = NFT_EXPR_SIZE(sizeof(struct nft_synproxy)),
 289         .init           = nft_synproxy_init,
 290         .destroy        = nft_synproxy_destroy,
 291         .dump           = nft_synproxy_dump,
 292         .type           = &nft_synproxy_type,
 293         .validate       = nft_synproxy_validate,
 294         .reduce         = NFT_REDUCE_READONLY,
 295 };
 296
 297 static struct nft_expr_type nft_synproxy_type __read_mostly = {
 298         .ops            = &nft_synproxy_ops,
 299         .name           = "synproxy",
 300         .owner          = THIS_MODULE,
 301         .policy         = nft_synproxy_policy,
 302         .maxattr        = NFTA_SYNPROXY_MAX,
 303 };
 304
 305 static int nft_synproxy_obj_init(const struct nft_ctx *ctx,
 306                                  const struct nlattr * const tb[],
 307                                  struct nft_object *obj)
 308 {
 309         struct nft_synproxy *priv = nft_obj_data(obj);
 310
 311         return nft_synproxy_do_init(ctx, tb, priv);
 312 }
 313
 314 static void nft_synproxy_obj_destroy(const struct nft_ctx *ctx,
 315                                      struct nft_object *obj)
 316 {
 317         nft_synproxy_do_destroy(ctx);
 318 }
 319
 320 static int nft_synproxy_obj_dump(struct sk_buff *skb,
 321                                  struct nft_object *obj, bool reset)
 322 {
 323         struct nft_synproxy *priv = nft_obj_data(obj);
 324
 325         return nft_synproxy_do_dump(skb, priv);
 326 }
 327
 328 static void nft_synproxy_obj_eval(struct nft_object *obj,
 329                                   struct nft_regs *regs,
 330                                   const struct nft_pktinfo *pkt)
 331 {
 332         const struct nft_synproxy *priv = nft_obj_data(obj);
 333
 334         nft_synproxy_do_eval(priv, regs, pkt);
 335 }
 336
 337 static void nft_synproxy_obj_update(struct nft_object *obj,
 338                                     struct nft_object *newobj)
 339 {
 340         struct nft_synproxy *newpriv = nft_obj_data(newobj);
 341         struct nft_synproxy *priv = nft_obj_data(obj);
 342
 343         priv->info = newpriv->info;
 344 }
 345
 346 static struct nft_object_type nft_synproxy_obj_type;
 347 static const struct nft_object_ops nft_synproxy_obj_ops = {
 348         .type           = &nft_synproxy_obj_type,
 349         .size           = sizeof(struct nft_synproxy),
 350         .init           = nft_synproxy_obj_init,
 351         .destroy        = nft_synproxy_obj_destroy,
 352         .dump           = nft_synproxy_obj_dump,
 353         .eval           = nft_synproxy_obj_eval,
 354         .update         = nft_synproxy_obj_update,
 355 };
 356
 357 static struct nft_object_type nft_synproxy_obj_type __read_mostly = {
 358         .type           = NFT_OBJECT_SYNPROXY,
 359         .ops            = &nft_synproxy_obj_ops,
 360         .maxattr        = NFTA_SYNPROXY_MAX,
 361         .policy         = nft_synproxy_policy,
 362         .owner          = THIS_MODULE,
 363 };
 364
 365 static int __init nft_synproxy_module_init(void)
 366 {
 367         int err;
 368
 369         err = nft_register_obj(&nft_synproxy_obj_type);
 370         if (err < 0)
 371                 return err;
 372
 373         err = nft_register_expr(&nft_synproxy_type);
 374         if (err < 0)
 375                 goto err;
 376
 377         return 0;
 378
 379 err:
 380         nft_unregister_obj(&nft_synproxy_obj_type);
 381         return err;
 382 }
 383
 384 static void __exit nft_synproxy_module_exit(void)
 385 {
 386         nft_unregister_expr(&nft_synproxy_type);
 387         nft_unregister_obj(&nft_synproxy_obj_type);
 388 }
 389
 390 module_init(nft_synproxy_module_init);
 391 module_exit(nft_synproxy_module_exit);
 392
 393 MODULE_LICENSE("GPL");
 394 MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
 395 MODULE_ALIAS_NFT_EXPR("synproxy");
 396 MODULE_ALIAS_NFT_OBJ(NFT_OBJECT_SYNPROXY);
 397 MODULE_DESCRIPTION("nftables SYNPROXY expression support");